Strategically interposed between the environment and host circulation, the airway epithelium can modulate the host response by acting either as a pro-inflammatory "sensor/amplifier" or anti-inflammatory "insulator/dampener". Airway inflammation is a two edged sword that must be precisely regulated. Thus, following pro-inflammatory stimulation, negative feedback mechanisms are typically invoked to restore homeostasis. Such adaptations are likely important in the setting of chronic microbial product exposure typical of chronic bronchitis and cystic fibrosis, but remain poorly understood. We hypothesize that adaptation is a key determinant of airway inflammation and that underlying mechanisms can be exploited as novel approaches for anti-inflammatory therapy. We show that the respiratory tract pathogen Pseudomonas aeruginosa activates the Toll-like receptor (TLR) pathway in airway epithelial cells, which become tolerant as manifest by decreased cytokine production and hypo-responsiveness to secondary stimulation. Gene array of Pseudomonas-tolerant versus -sensitive airway epithelial cells demonstrated induction of 3 prominent negative regulators of TLR signaling. To understand the role and consequences of airway epithelial adaptation, we propose the following Specific Aims: 1) To define the role of IRAKM, A20 and DUSP5 in airway epithelial tolerance to Pseudomonas aeruginosa, and 2) To determine if inhibitors of the response to Ps. a. can blunt airway inflammation in vivo without rendering the host susceptible to lung destruction or systemic dissemination of infection. To accomplish these aims, we will first test candidate tolerance-inducing genes on NF-KB- and AP-1- dependent transcription in a human airway epithelial cell line, with verification in primary well-differentiated cells. We will then determine the level of action in the signal transduction cascade and will explore inhibitory mechanisms. Finally, we will determine if manipulating tolerance-inducing genes in vivo can exploit a therapeutic window to decrease inflammation without excessively compromising host defense. A greater understanding of airway epithelial adaptation, and its functional outcome, provides a logical basis for the design of novel anti-inflammatory therapies.